Floor protectors for casters

ABSTRACT

To protect floors against marks or damage from casters , a shrinkable tire, for example, a piece of heat-shrink tubing, in its unshrunk condition, is fitted around the caster circumference and then is shrunken. The dimensions and shrinkage ratio of the shrinkable tire are selected such that, when shrunken onto the caster, the tire grips the caster securely. If desired, the frictional grip between the tire and the caster circumferential surface may be enhanced by applying to the interior of the unshrunk tire a hot-melt adhesive which will be activated by the heat applied to shrink the tire. Additionally or alternatively, the width of the tire may be greater than the width of the caster so that, when the tire has been shrunken onto the caster, marginal portions of the tire form flanges gripping the caster on opposite sides.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional patent application Ser. No. 61/383,577 filed Sep. 16, 2010, the entire contents of which are incorporated herein by reference. This application also claims priority from U.S. Provisional patent application Ser. No. 61/383,572 filed Sep. 16, 2010, the entire contents of which are incorporated herein by reference. This application is related to U.S. patent application Ser. No. 12/082,054 filed Apr. 8, 2008, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to floor protectors, and, more particularly, floor protectors for use with casters for attaching, or attached, to a movable object to protect the floor when the object is moved. Examples of such objects include furniture, such as beds, chairs, tables, desks, privacy screens, room dividers, partitions and storage cabinets for files; and other objects such as equipment stands, display stands, trucks, carts, trolleys, and so on.

In this specification the term “caster unit” embraces one or more casters rotatably mounted in or on a support frame that is attachable by a swivel to the movable object. Such a castor may be disc-, ball- or ballel-shaped and sometimes is called a “caster wheel”, especially when dish-shaped.

BACKGROUND

Furniture leg floor protectors have been in use for many years to avoid damage to floors when a piece of furniture or other movable object is moved. They may also reduce noise in the classroom where children tend to move their desks and chairs around often making an irritating noise. Examples of floor protectors for attachment to the foot portion of a furniture leg, for example, a chair leg, are disclosed in the following United States patents and United States published patent applications: US 2005/0003723 (Brouard et al.), US 2008/0148522 (Beshore), US 2007/0234507 (Vorpahl), U.S. Pat. No. 2,865,133 (Hoven et al.), U.S. Pat. No. 6,405,982 (Ferencz), and U.S. Pat. No. 6,754,934 (Shiffler), US 2007/0220703 (LaPointe et al.), US 2008/0179471 (Verdelli), US 2008/0209686 (Lang), U.S. Pat. No. 7,124,986 (Bailey), US 2004/0123421 (Bushey), US20050115022, (Desmarais—the present inventor), US20080258023 (Desmarais—the present inventor).

The need to protect floors may also arise where the furniture or other movable object is equipped with caster units for ease of movement. In the home or a hospital setting, for example, such caster units may be fitted to beds. In the office setting, many office chairs are mounted upon a pedestal having, typically, five legs each with a caster unit. Some caster wheels are made of hard black synthetic plastics material, for example polyurethane, which may leave marks upon, or physically damage, certain types of flooring. It is known to provide plastic mats beneath such office chairs both to protect the floor and, in some cases, guard against the build-up of static electricity. Disadvantages of such mats, however, is that they are relatively expensive, unsightly and may impair movement of the chairs.

It is known to equip the caster with a cover of relatively soft material which is less likely to cause damage to, or mark, the floor. For example, Products of Maximus LLC markets a caster tire cover under the trademark CasterBooties which involves a leader strap to pull the cover onto a caster in the form of a wheel, an elastic band each side to hold the cover onto the caster, an over flap, an under flap, and Velcro™ fasteners. According to their web site at http://www.tirebooties.com/CasterBooties_Caster_Tire_Covers.html, in addition to being complicated, the cover is not recommended for steel caster wheels or dual wheels and will not fit on casters with wheel brakes. (cf. web page appended to this description.)

United States patent publication No. 2007/0062001 (Bushey et al.) discloses a caster wheel cover comprising a generally cylindrical floor-engaging member having sidewalls projecting from opposite edges to define a channel which receives the outer surface portion of the caster wheel. The cover is installed by wrapping it around the circumference of the caster wheel. In one embodiment, the cover can be opened and closed, like a bracelet, to enable it to be fitted onto the caster wheel. In another embodiment, the cover is a complete circle and one sidewall has notches to allow it to flex and facilitate installation of the cover. Yet another embodiment is a complete circle but with no notches; instead the inner surfaces of the sidewall are laterally spaced from respective sides of the wheel. Such a caster wheel cover in the form of a complete circle, without notches, is marketed by Expanded Technologies LLC under the trademark CasterTire™. According to installation instructions on their web site at http://www.expandedtechnologies.comicaster_tire_inst.html, (cf. web page appended to this description) the caster tire is installed in much the same way that a car tire is installed, using a tire lever to pry the tire over the wheel. The installation instructions include a tip, namely “If having trouble with installation, try placing tires in a bucket of hot tap water. The hot water will make the tires more pliable and easier to install.”

There remains a need, therefore, for a floor protector for a caster that not only is durable and secure once installed, but also can be installed easily and, once worn, replaced easily.

An object of the present invention is to overcome or at least mitigate problems associated with such caster covers or tires and to provide a floor protector for casters which combines ease of installation with a secure grip once it has been installed.

DISCLOSURE OF INVENTION

To this end, embodiments of the present invention employ a shrinkable tire, for example, a piece of heat-shrink tubing, which, in its unshrunk condition is fitted around the caster and then is shrunken onto the caster circumferential surface, the dimensions and shrinkage ratio of the shrinkable tire being such that, when shrunken onto the caster, the tire grips the caster securely.

In this specification, the word “unshrunk” will be used to describe the condition of the tire before it has been shrunk, and the word “shrunken” will be used to describe the tire after it has been shrunk. This does not preclude, however, the tire having been pre-shrunken partially to the “unshrunk” size.

According to one aspect of the present invention, there is provided a floor protector adapted for use on a caster of a caster unit attachable or attached to an item of furniture or other movable objects, the floor protector comprising a tire of shrinkable material that can be shrunk by a predetermined shrinkage ratio by application of heat or by other suitable means, the tire having, at normal room temperatures, a predetermined unshrunk cross-sectional size that allows the tire to be fitted around the circumference of the caster said cross-sectional size and, the shrinkage ratio being such that, when shrunk, the tire will conform to the circumference of the caster and adhere thereto.

According to another aspect of the present invention, there is provided a method of installing a floor protector onto a caster of a caster unit attachable or attached to an item of furniture or other movable equipment, comprising the step of fitting over the circumference of the caster an unshrunk tube of shrinkable material, the shrinkable material having a shrinkage ratio such that, when shrunk, the tire will conform to the caster and adhere thereto, the method further comprising shrinking the tire by application of heat or by other suitable means at least until the tire has conformed to the underlying surface of the caster to such an extent as to secure the floor protector to said underlying surface.

Preferably, in embodiments of either aspect, the shrinkable tire is made of so-called heat-shrink tubing material which shrinks when heated, for example polyurethane, polyolefin, fluoropolymer (such as fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (e.g., Kynar™, polyvinylchloride (PVC), neoprene, silicone elastomer and fluoroelastomer (e.g., Viton™).

In embodiments of either aspect of the invention, the unshrunken tire may have a width that is greater than the axial width of a rim portion of the caster to such an extent that, when the tire has been shrunken, opposite margin portions of the shrunken tire form flanges that extend radially inwards to engage respective opposite sides of the rim portion of the caster to resist axial movement of the tire relative to the caster.

Some casters have an edge profile that is larger in diameter at the middle than the sides. For example, some casters are generally ball-shaped, or generally barrel-shaped, while others have a circumferential ridge around the middle of the circumferential surface of the caster. The width of the tire may be selected so that, once the tire has been shrunken onto the caster, opposite edge portions of the tire will extend radially-inwardly and resist axial movement of the tire relative to the caster wheel. The heat-shrink material will become denser and stiffer as it is shrunk, so the radially inwardly extending portions will provide a mechanical locking effect to resist removal of the floor protector. Where the caster wheel has such an edge profile, the width of the tire may be great enough for opposite edge portions to extend not only radially inwardly to engage opposite sides of the larger-diameter middle of the caster wheel but less than the width of the caster wheel; i.e., there will be no flanges extending inwards on opposite sides of the rim portion of the caster. Conversely, the tire may be wide enough to conform not only with the sides of the larger-diameter middle of the caster wheel (e.g., ridge, rib or lesser-diameter parts of the barrel-shaped surface) but also extend radially inwards on each of the opposite sides of at least a rim portion of the caster.

In embodiments of either aspect of the invention, at least part of the interior surface of the tire may be provided with an adhesive so that, once the tire has been shrunk onto the caster wheel, the adhesive bonds the tire to the caster wheel and provides additional security against the tire being accidentally dislodged, at least partially. Where the tire comprises heat-shrink material, the adhesive may be a heat-sensitive (hot-melt) adhesive that melts at temperatures similar to those required to shrink the tire; the hot-melt adhesive then being melted (activated) contemporaneously with the shrinking of the tire, conveniently using the same heat source.

Preferably the shrinkable tire material is selected, both in terms of its shrinkage characteristics and dimensions, including thickness, so that the shrunken tire may conform closely to the exterior of the caster wheel, both to provide a desired gripping (e.g. frictional) force and avoid, at least to some extent, an unsightly result. The tire material may be transparent, also for aesthetic reasons.

Further features and advantages of floor protectors embodying the present invention will be set out in the following description of preferred embodiments of the invention, taken in conjunction with the accompanying drawings, which is provided by way of example only.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a pictorial rear view of a caster unit having two casters of the kind fitted to a furniture leg;

FIG. 2 is a rear view of the caster unit of FIG. 1 showing a narrow tire of shrinkable synthetic plastics material alongside one of the casters prior to installation upon it;

FIG. 3 is a view similar to FIG. 2 with the unshrunken tire placed over the caster;

FIG. 4 is a view similar to FIG. 3 showing the shrinkable tire shrunken onto the caster; and

FIG. 5 is a pictorial rear view of the caster with the shrinkable tire installed;

DETAILED DESCRIPTION PREFERRED EMBODIMENTS

FIG. 1 shows a typical caster unit 101 having two casters 102A and 102B on a common axle (not shown) supported by a support member 103 itself carried by a swivel 104 which, in use, will allow the support member 103 to rotate about a generally vertical swivel axis. As shown, the swivel 104 comprises a spigot for attachment to the foot portion of a furniture leg for example the leg of an office chair (not shown), typically by insertion into a complementary socket in the end of the leg. Alternatively, the swivel 104 may comprise a flat plate having screw holes for attachment to the end of a furniture leg, to the underside of a cabinet, and so on. As is customary, the axis of swivel 104 is eccentric to the rotation axis of the common axle so that the caster unit 101 can swivel around the swivel axis as the furniture or other object is moved. For convenience, the following description is of one tire being fitted to caster 102A, but it will be understood that a similar tire would usually be fitted, in the same manner, to caster 102B.

Thus, FIG. 2 shows the same caster unit 101 with a floor protector in the form of a tire 105 of shrinkable thermoplastic material, specifically a short piece of heat-shrink tubing, alongside caster wheel 102A. The shrinkage ratio and cross-sectional size , i.e., diameter, of the tire 105 are chosen so that, unshrunken, it is large enough to fit around the circumference of the caster 102A, possibly with a little stretching; but once it has been shrunk, the tire 105 grips the circumference of the caster 102A firmly and securely enough that it will not be dislodged readily during normal usage.

The majority of commercial office casters are from 1.75″ to 2.25″ in diameter and it has been found that a suitable tire 105 could be cut from a tube of shrink material 2.25″ in diameter and from 1 mm to 2 mm thick. The thickness is quite important, since a thinner tire will be easier to install onto the caster wheel, but will wear down more quickly when in use. A shrinkage ratio of 2:1 means, theoretically, that a tire having a diameter of 2.25″ before shrinking could grip a caster as small as 1.125″ in diameter when shrunken. For better grip, however, it would be possible, and might be preferable, to use shrinkable tubing material having a 3:1 or 4:1 shrinkage ratio. Also, a greater shrinkage ratio, such as between 3:1 and 4:1, might allow one size of shrinkable tubing tire to fit several sizes of caster.

It has also been found that, for a caster having a width of ⅜″ inch, cutting the shrink tubing into bands (tires) that are ¾″ wide allows for marginal flanges 106 for engaging the opposite sides of the caster to resist sheer forces when the caster is rolling with a person's weight applied to the caster.

As shown in FIG. 3, which shows the tire 105 in place around the caster 102A, the width w_(t) of the tire 105 is greater than the width w, of the caster 102A so that, when the tire is centered, equal margin portions overhang the caster on opposite sides of its rim portion. When the tire 105 has been shrunk onto the caster 102A, and the medial portion of the tire 105 is in contact with the circumferential surface of the caster 102A, the opposite margin portions 106 of tire 105 form flanges extending radially inwards to grip the respective opposite side faces of the rim portion of the caster 102A, as shown in FIGS. 4 and 5. In this condition, the heat-shrink material of the shrunken tire 105 is relatively inelastic and the flanges 106 mechanically resist forces tending to dislodge the tire 105 from the caster 102A.

Some caster units have casters which are not discs of constant diameter, i.e., they may be ball-shaped or barrel-shaped, or have at least one circumferential ridge extending around the middle of the circumferential surface of the caster. In such a case, the tire 105 may not need to be wider than the caster 102A, providing it conforms to the circumferential surface each side of its maximum diameter, and/or, where applicable, the opposite sides of the ridge, and mechanically resists axial movement of the tire 105. On the other hand, the tire 105 may be wider than the caster so that, when it has been shrunk into conformity with the circumferential surface of the caster to provide some mechanical locking effect, it will also form marginal flanges 106 to engage opposite sides of the rim portion of the caster, as previously described, and provide additional security against the tire 105 being dislodged.

If desired, heat-sensitive (hot-melt) adhesive can be provided on the interior of the unshrunken tire 105. The adhesive may be selected so that the heat required to shrink the tire 105 onto the rim of the caster 102A will be sufficient to melt or activate the heat-sensitive (hot-melt) adhesive contemporaneously. Compositions resistant to plasticizers, usually based on polyamides, are needed for gluing PVC. There are also many low temperature hot melt adhesives that could be used if heat shrink materials other than PVC are used. The adhesive provides additional security against the tire 105 being dislodged during normal use. It may be preferable for the adhesive to be transparent when set, especially when used with a transparent tire 105. The shrink material may also include a UV stabilizer, especially if the object is to be used outdoors or otherwise exposed to sunlight and especially if the tire is transparent.

In some cases, it may be possible to select the heat-shrink material of the tire and the material of the circumference of the caster so that the applied heat not only causes the tire 105 to shrink but also causes either or both of the materials at the interface between the caster and the tire to melt and bond (weld). Once the caster and tire cool, they will be bonded together without the use of a separate adhesive applied to the inner surface of the tire.

It is envisaged that the use of adhesive, or heating until one or both of the juxtaposed surfaces of the tire and wheel melt(s) and bond(s) or weld(s), might be particularly desirable if the width of the tire 105 is less than the width of the caster, especially if the caster has a constant diameter.

Although the caster unit 101 shown in FIGS. 1 to 5 is of the type in which the swivel 104 has a spigot for insertion into a socket in the furniture leg, the invention embraces floor protection for other types of caster unit, such as those in which the support member is attached by a bearing to a flat plate having screw-holes enabling it to be attached, by screws or bolts, to the underside of the foot of a furniture leg or underside of a cabinet, and so on.

Heat-shrink materials presently readily available may be shrunk using hot air supplied by, for example, a small butane torch or heat gun, an electric hot air paint stripper, a commercial (high temperature) hair drier, or other suitable heat source. The choice of heat source will depend upon the characteristics of the heat-shrink material and the size of the caster . The heat will be applied evenly and be maintained at least at 100° C. for PVC tubing or 80° C. for polyolefin, for example. A variety of heat-shrink materials are commercially available at this time, most of them in the form of (extruded) tubing which can be cut to length to form an unshrunk tire 105. Examples include polyurethane, polyolefin, fluoropolymer (such as fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (e.g., Kynar™), polyvinylchloride (PVC), neoprene, silicone elastomer and fluoroelastomer (e.g., Viton™). PVC is preferred for some embodiments of the present invention because it is less affected by ultraviolet radiation, so the casters would be more suitable for use outdoors. Also, PVC is generally harder and more abrasion-resistant. Polyolefin might be preferred, however, where it is desirable/necessary to use a heat source delivering lower shrink temperatures.

It should be appreciated that heat-shrink material that is presently available commercially is formed by extrusion, which requires lower temperatures (e.g. less than about 80° C.) than injection moulding temperatures (e.g. 100-150° C.) because the extruded tire tubing must be firm enough to pull whereas the injected plastics material must be viscose enough to flow.

On the other hand, if neither adhesive is used, nor thermal bonding (welding) is used, the tires could be replaced more easily, when worn, simply by cutting them off.

Although it is preferred to use PVC heat-shrink material in embodiments of the present invention, it should be noted that other shrinkable materials might be used instead, according to their specific composition and characteristics and suitability for particular floor protector applications. Known heat-shrink tubing is manufactured from thermoplastic material including, for example, polyurethane, polyolefin, fluoropolymer (such as fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (e.g., Kynar™), polyvinylchloride (PVC), neoprene, silicone elastomer and fluoroelastomer (e.g., Viton™).

It is known to use heat-shrink tubing and heat-shrink end caps in the electrical industry around connections between electrical conductors and terminals, to provide insulation, abrasion resistance and environmental protection. Heat-shrink materials may shrink to as little as one third or one quarter of their original size and may shrink at temperatures which can be obtained using a heat source that is relatively readily available, such as a small butane torch, an electrical hot air paint-stripper or a hair dryer. Generally, professional- or commercial-grade hair driers would be preferred because domestic hair driers operate at lower air temperatures and/or flow rates than commercial hair driers, which limits their use with heat-shrink materials that are commercially available at this time. Nevertheless, use of a domestic hair dryer or other heat source is not precluded if it can provide the required flow of air at a sufficiently high temperature.

It should be appreciated that there are different kinds of heat-shrink material. Some such materials contain many monomers which polymerize when the tubing is heated. As the monomers cross-link and occupy less space, the density of the material increases and the volume of the material shrinks. On the other hand, so-called expansion-type heat-shrink materials comprise polymers and are stretched physically to the expanded or “unshrunk” state. Application of heat causes the polymers to “relax” and the material to shrink.

INDUSTRIAL APPLICABILITY

Floor protectors embodying the present invention may overcome problems with known floor protectors for casters which are so thick that they may prevent the caster from rolling freely and much too difficult to install as a lot of force is required in order to slide the protector over the caster. 

1. A floor protector adapted for use on a caster of a caster unit attached or attachable to an item of furniture or other movable object comprises a tire of shrinkable material that can be shrunk by a predetermined shrinkage ratio by application of heat or by other suitable means, the tire having, at normal room temperatures, a predetermined unshrunk cross-sectional size that allows the tire to be fitted around the circumference of the caster, the cross-sectional size and the shrinkage ratio being such that, when shrunk, the tire will conform to the caster and adhere thereto.
 2. A floor protector according to claim 1, wherein the unshrunk tire has a width selected so that, when the tire has been shrunken onto the caster, opposite margin portions of the shrunken tire extend radially inwards to engage respective opposite edge portions of opposite sides of a rim portion of the caster and provide mechanical resistance against axial movement of the tire relative to the caster.
 3. A floor protector according to claim 1, adapted for fitting to a caster comprising a circumferential surface having a profile with a medial portion greater in diameter than marginal portions, the unshrunk tire having a width such that, when the tire has been shrunken onto the caster, the tire conforms to surfaces of the caster each side of its maximum diameter to provide mechanical resistance to axial movement of the tire relative to the caster wheel.
 4. A floor protector according to claim 2, adapted for fitting to a caster comprising a circumferential surface having a profile with a medial portion greater in diameter than marginal portions, the unshrunk tire having a width such that, when the tire has been shrunken onto the caster, the tire conforms to surfaces of the caster each side of its maximum diameter to provide mechanical resistance to axial movement of the tire relative to the caster wheel.
 5. A floor protector according to claim 3, adapted for fitting onto a caster comprising a circumferential surface having a stepped profile providing a larger diameter central section and smaller diameter sections either side of the central section defining shoulders between the central section and the smaller diameter sections, the size and shrinkage ratio of unshrunk tire being such that, when the tire has been shrunken onto the caster , parts of the tire engage respective shoulders to provide mechanical resistance against axial movement of the tire relative to the caster.
 6. A floor protector according to claim 3, adapted for fitting to a caster comprising a circumferential surface having a barrel-shaped profile, the size and shrinkage ratio of the unshrunk tire being selected so that portions of the shrunken tire either side of a maximum diameter of the caster will grip underlying lesser diameter surfaces of the caster wheel to provide mechanical resistance to axial movement of the tire relative to the caster.
 7. A floor protector according to claim 1, wherein said shrinkable material is heat-shrinkable and at least part of the interior of the floor protector is provided with a heat-sensitive (hot-melt) adhesive arranged to melt at temperatures required to shrink the heat-shrinkable material such that the adhesive will be melted contemporaneously with the shrinking of the tire, and adhere the shrunken tire to said caster.
 8. A floor protector according to claim 1, wherein the shrinkable material comprises a thermoplastic material, for example polyurethane, polyolefin, fluoropolymer (such as fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (e.g., Kynar™), polyvinylchloride (PVC), neoprene, silicone elastomer and fluoroelastomer (e.g., Viton™).
 9. A floor protector according to claim 1, wherein the shrinkable material is heat-shrinkable and both the heat-shrinkable material and a circumferential surface of the caster have melting points such that application of heat not only shrinks the tire onto the caster but also causes the interior surface of the tire and underlying surface of the caster to fuse together and, once cooled, bond the tire to the caster.
 10. A floor protector for attachment to a foot portion of an item of furniture or other moveable item, or to a caster of a caster unit attached or attachable to an item of furniture or other movable item, the floor protector comprising a tube of heat-shrinkable material having, at normal room temperatures a cross-sectional size sufficient to fit onto said foot portion or caster, and a shrinkage ratio such that, when shrunken, the tube will grip the foot portion or caster, at least part of the interior of the tube being provided with heat-sensitive or hot-melt adhesive that will melt at temperatures required to shrink the tube onto the foot portion or caster, such that the adhesive will melt contemporaneously with the shrinking of the tire and, when cooled, adhere the shrunken tire to said foot portion or caster.
 11. A method of installing a floor protector onto a caster of a caster unit attached or attachable to furniture or other movable equipment, comprising the steps of: fitting over the circumference of the caster an unshrunk tire comprising a shrinkable material; the shrinkable material having a shrinkage ratio greater than a ratio between a cross-sectional size of the unshrunk tire and a maximum diameter of the caster wheel; applying heat or other suitable means to cause the tire to shrink at least until the tire conforms to the underlying surface of the caster to such an extent as to secure the floor protector to said underlying surface.
 12. A method according to claim 10, wherein a width of the unshrunk tire is selected so that, when the tire has been shrunken onto the caster , opposite margin portions of the shrunken tire extend radially inwards to engage respective opposite edge portions of opposite sides of the caster and provide mechanical resistance against axial movement of the tire relative to the caster.
 13. A method according to claim 12, for fitting a tire to a caster comprising a circumferential surface having a profile with a medial portion greater in diameter than marginal portions, wherein a width of the unshrunk tire is selected such that, when the tire has been shrunken onto the caster, the tire conforms to surfaces of the caster each side of its maximum diameter to provide mechanical resistance to axial movement of the tire relative to the caster.
 14. A method according to claim 12, wherein a width of the unshrunk tire is selected so that, when the tire has been shrunken onto the caster , opposite margin portions of the shrunken tire extend radially inwards to engage respective opposite edge portions of opposite sides of the caster and provide mechanical resistance against axial movement of the tire relative to the caster.
 15. A method according to claim 12, for fitting a tire onto a caster comprising a circumferential surface having a stepped profile providing a larger diameter central section and smaller diameter sections either side of the central section defining shoulders between the central section and the smaller diameter sections, wherein a width and shrinkage ratio of the unshrunk tire are selected such that, when the tire has been shrunken onto the caster, parts of the tire engage respective shoulders to provide mechanical resistance against axial movement of the tire relative to the caster.
 16. A method according to claim 13, for fitting a tire to a caster comprising a circumferential surface having a barrel-shaped profile, wherein the shrinkage ratio of the unshrunk tire is selected so that portions of the shrunken tire either side of a maximum diameter of the caster will grip underlying lesser diameter portions of said circumferential surface of the caster to provide mechanical resistance to axial movement of the tire relative to the caster.
 17. A method according to claim 11, wherein at least part of the interior of the tire is provided with a heat-sensitive (hot-melt) adhesive arranged to melt at temperatures required to shrink the tire such that the application of heat to shrink the tire onto the caster contemporaneously melts the adhesive so that, on cooling, the shrunken tire is adhered to said caster by said adhesive.
 18. A method according to claim 11, wherein the shrinkable material comprises polyvinylchloride.
 19. A method according to claim 11, wherein the tire comprises heat-shrinkable material and respective interior and exterior surfaces of the tire and the caster have similar melting points, the method comprising the steps of applying sufficient heat to shrink the tire onto the caster and cause the said interior and exterior surfaces to fuse together, and cooling the tire and caster so that the fused interior and exterior surfaces adhere the tire to the caster.
 20. A method of attaching a floor protector to a foot portion of an item of furniture or other movable item, or to a caster of a caster unit attached or attachable to an item of furniture or other movable item, the method comprising the steps of fitting onto the foot portion or caster a tube of unshrunk heat-shrinkable material having heat-sensitive or hot-melt adhesive applied to at least a part of its interior, applying sufficient heat to shrink the tube of heat-shrinkable material onto the foot portion or caster and cause the adhesive to melt and on cooling the tube and foot portion or caster so that the cooled adhesive adheres the tube to the foot portion or caster. 